Are these betting calculators free?
Yes, all six are free, need no account, and run entirely in your browser. Nothing you type is sent to a server or stored anywhere.
Betting calculators
Free, no signup. Last updated 15 August 2026.
Six tools for the arithmetic behind a bet. Everything runs in your browser, nothing is stored and nothing is sent anywhere. They are free because the maths is not the hard part of betting, discipline is.
Odds converter
Decimal, fractional and American, plus the probability each price implies.
Open →Implied probability and margin
Turn prices into percentages and reveal the bookmaker overround on a market.
Open →Expected value
Test whether a price is worth taking, given your own estimate of the chance.
Open →Kelly stake
Size a bet in proportion to your edge, with half and quarter Kelly fractions.
Open →ROI and yield
Measure how efficient your betting is, and how big a sample it takes to matter.
Open →Accumulator
Combined odds, payout, and the real chance every leg lands.
Open →Which one do I need?
If you are starting out, the odds converter and the implied probability calculator are the two that change how you read a betting slip. Together they turn a price into a percentage and show you what the bookmaker is charging for the privilege.
If you already have a view on a match, the expected value calculator tells you whether the price justifies the bet, and the Kelly calculator tells you how much to put on. If you are reviewing how a season went, use the ROI calculator and pay more attention to the number of bets than to the percentage.
Frequently asked questions
What is the most useful betting calculator for a beginner?
The implied probability calculator. Converting odds into a percentage, and seeing how far a market exceeds 100 percent, is the single change that makes betting prices legible rather than mysterious.
Do these work for any sport?
Yes. The arithmetic of odds, probability, expected value and staking is identical across football, basketball, tennis, racing and everything else. Only the way lines are presented differs.
We do this maths on every pick
Three value picks a day in the free Telegram, each published with its price and stake, and every one of them ends up on the public record.
Join the free Telegram →18+. These tools are for information only. Betting involves risk and any bet can lose. Nothing here is financial advice.
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